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Genetics > Chapter 13: The Genetic Code and Transcription > Flashcards

Chapter 13: The Genetic Code and Transcription Flashcards

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1
Q

What polymerase is responsible for transcription?

A

RNA polymerase

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2
Q

True or false: a primer is needed for both DNA replication and transcription.

A

False. A primer isn’t needed for transcription because it uses RNA polymerase, not DNA polymerase.

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3
Q

Does RNA polymerase use DNA or RNA nucleotides for transcription?

A

RNA nucleotides

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4
Q

What four things are required for transcription?

A
  1. All four ribonucleotide 5’ triphosphates
  2. A DNA template strand
  3. 5’ to 3’ synthesis
  4. Control sequences
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5
Q

RNA polymerase is a _____, which is composed of multiple subunits.

A

holoenzyme

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6
Q

What does the sigma subunit of the RNA polymerase holoenzyme do?

A

It recognizes the promotor sequences on the DNA.

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7
Q

This control sequence is present in all genes and does not get copied, but signals the polymerase to start at that site.

A

Promoter

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8
Q

Prokaryotes only have _____ holoenzymes, while eukaryotes have _____.

A

five; thirty

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9
Q

How does polymerase know which DNA strand to copy?

A

Only one strand has the promoter sequence.

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10
Q

Where is the promoter sequence located?

A

Towards the 5’ end.

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11
Q

Does the sigma subunit stay with the holoenzyme as it elongates the chain?

A

No, it falls off after the holoenzyme has found the promoter and starts working.

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12
Q

These are sequences of DNA that are similar in different genes of the same organism or in related organisms.

A

Consensus sequences

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13
Q

What are the two consensus sequences in prokaryotes?

A

-10 TATAAT and -35 TTGACA

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14
Q

What is the Pribnow box, and where is it located?

A

TATAAT, located at -10.

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15
Q

Where is the TTGACA consensus sequence located?

A

-35

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16
Q

What are the two consensus sequences in eukaryotes?

A

-35 TATAAATA and -80 GGCCAATCT

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17
Q

Where is the TATAAATA sequence located?

A

-35

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18
Q

Where is the GGCCAATCT sequence located?

A

-80

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19
Q

What’s the CAAT box?

A

GGCCAATCT

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20
Q

Why are consensus sequences so heavy on A’s and T’s?

A

They have only two hydrogen bonds, making them easier to open.

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21
Q

How is efficiency affected by protein demand?

A

Proteins in high demand must be transcribed very efficiently, while low demand ones can be off by a nucleotide or two because they aren’t needed as much.

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22
Q

What are the two types of promoters?

A

Focused and dispersed

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23
Q

This type of promoter appears only once in the gene, meaning there’s only one start site for polymerase so it always starts on the same spot.

A

Focused

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24
Q

This type of promoter appears multiple times, offering several start sites.

A

Dispersed

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25
Q

This type of promoter appears in both prokaryotes and eukaryotes and is highly conserved.

A

Focused

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26
Q

This type of promoter appears only in eukaryotes.

A

Dispersed

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27
Q

What does a transcription termination site in prokaryotes usually look like?

A

A string of A’s preceded by a palindrome.

28
Q

How does polymerase know when to stop transcribing in prokaryotes?

A

The palindrome at the end of the sequence makes a little hairpin loop by base pairing with itself, and when polymerase hits it, it knows to copy it and then stop.

29
Q

What happens in prokaryotes after the mRNA comes out of the polymerase?

A

Since there’s no nucleus, the ribosomes are ready and waiting for the mRNA to wrap around them to be translated into proteins.

30
Q

What happens in eukaryotes after the mRNA comes out of the polymerase?

A

tRNAs are made in the nucleus, and then they go out to the ribosomes to be made into protein.

31
Q

How can you tell a prokaryotic mRNA from a eukaryotic mRNA just by looking at it?

A

Prokaryotic ones will have ribosomes, while eukaryotic ones will not.

32
Q

Does polymerase have to finish transcribing the RNA before another one can start?

A

No, multiple polymerases can be on at once. They jump on wherever there’s promoter.

33
Q

What happens to the promoter once it falls off?

A

It’s ready for the next.

34
Q

How can you tell between a really efficient gene and a less efficient gene by looking at transcription?

A

More efficient genes will have a lot of mRNAs coming off of them, because they are being transcribed quickly by multiple polymerases. Less efficient ones will only have a few.

35
Q

In _____, transcription and translation occur in the same place, while in _____, it occurs in two different locations (the nucleus and the ribosome, respectively).

A

prokaryotes; eukaryotes

36
Q

How many polymerases are there in eukaryotes?

A

Three

37
Q

This polymerase makes rRNA in the nucleolus.

A

Polymerase I

38
Q

This polymerase makes mRNA and snRNA in the nucleoplasm.

A

Polymerase II

39
Q

This polymerase makes 5S rRNA and tRNA in the nucleoplasm.

A

Polymerase III

40
Q

This is a sequence at the 5’ end of an mRNA, right before translation initiation begins, that helps facilitate translation.

A

Leader sequence

41
Q

This is a sequence on an mRNA on the 3’ end where translation termination begins.

A

Trailer

42
Q

True or false: In eukaryotes, RNA made by polymerase is not yet ready to be made into protein directly after transcription.

A

True

43
Q

What three steps must be completed before RNA is ready for translation in eukaryotes?

A
  1. It must be transcribed into pre-mRNA by polymerase, making a copy of the DNA strand.
  2. A cap and tail must be added.
  3. The mRNA’s introns must be removed and its exons spliced together.
44
Q

How stable are mRNAs, and why?

A

They’re very delicate and have a short lifetime, because as long as they are around, proteins will be translated from them. If they were around forever, we’d make that protein forever.

45
Q

Proteins that are factors that help with transcription initiation are called _____.

A

Transcription factors

46
Q

This transcription factor binds directly to the TATA box, recruiting other transcription factors to form the pre-initiation complex.

A

TFIID

47
Q

This is a cap placed on new RNAs during DNA processing as soon as it comes off the polymerase.

A

7-methylguanine

48
Q

This has three phosphates attached to it, but the phosphodiester bond is 5’ to 5’.

A

7-methylguanine

49
Q

Does the poly-A tail get put on before or after the cap?

A

After.

50
Q

True or false: Polymerase stops when it gets to the polyadenylation signal, and the tail is placed on the end of the new RNA.

A

False. Polymerase keeps going through that signal, the cleavage signal, and the stop signal.

51
Q

This enzyme sees the poly-A signal get transcribed and cuts the RNA directly after.

A

Clipping enzyme complex, or endonuclease

52
Q

True or false: endonuclease is a separate unit from the polymerase.

A

False. It is attached to it.

53
Q

What happens after endonuclease cuts the RNA?

A

A string of A’s gets put on the end.

54
Q

What happens to the polymerase after endonuclease clips the new RNA strand off?

A

It keeps going down the DNA strand, making an RNA strand.

55
Q

What stops polymerase after the RNA is clipped?

A

Exonuclease nibbling back the RNA and hitting polymerase.

56
Q

This enzyme jumps on the strand that polymerase continues to make after the RNA has been clipped and polyadenylated, then nibbles the extra RNA. When it reaches polymerase, transcription stops.

A

Exonuclease

57
Q

_____ is intron removal from pre-RNA to make mRNA.

A

Splicing

58
Q

True or false: intron removal occurs only in prokaryotes.

A

False. Prokaryotes do not have introns and exons; this only occurs in eukaryotes.

59
Q

How are introns removed?

A

They form loops with the help of proteins, then get cut off by an enzyme. The exons are then sealed together by ligase.

60
Q

True or false: introns are much larger than exons.

A

True.

61
Q

Why are introns so much larger than genes if they’re just going to be removed?

A

They allow a single gene to make more than one protein.

62
Q

This stands for small nuclear ribonuclearprotein particles.

A

snRNP

63
Q

This is composed of multiple snRNPs assembled at splicing junctions.

A

Spliceosome

64
Q

What is the role of the spliceosome?

A

It pulls the ends of the intron together, cuts it, and splices the exons.

65
Q

True or false: Intron removal can be off by a nucleotide or two.

A

False.

66
Q

Why must intron removal be incredibly precise?

A

If it’s off by even one nucleotide, you’re getting into the exons and that changes the sequence, introducing a mutation.

Genetics (6 decks)

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